1. Field of the Invention
The present invention relates generally to transverse connectors used in spinal fixation systems. The invention comprises assemblies that are coupled to spinal rods, plates, or other elongate members to provide stability to a construct. The invention may be configured so that multiple transverse connectors may be used along the vertebral column.
2. Description of the Related Art
Advancing age, as well as injury, can lead to degenerative changes in the bones, discs, joints and ligaments of the spine, producing pain and instability. Under certain circumstances, alleviation of the problems can be provided by performing spinal fusion. Spinal fusion is a surgical technique where two or more vertebrae of the spinal column are fused together to eliminate the motion between the fused vertebrae. Spinal fusion is used to treat conditions where the spine exhibits instability. Spine instability may result from causes such as fracture, scoliosis and spondylolisthesis, where one or more vertebrae move in a forward direction relative to the other vertebrae. Spinal fusion with discectomy is also performed for herniations of the discs. This surgery involves removal of the affected disc and fusion of the adjacent vertebrae. Traditionally, bone grafts have been used to fuse the vertebrae, but various types of vertebral implants have also been used.
The use of fixation systems for achieving spinal fusion is well established. One of the more common fixation systems is the pedicle screw fixation system. In this fixation system, pedicle screws are inserted into two or more vertebrae and interconnected with a rod or other elongate member. The screws are rigidly connected to the elongate member so that the fixation system greatly reduces motion between the adjoining vertebrae. Multiple fixation systems may be utilized to achieve greater strength and stability. Other types of fixation systems use different vertebrae attachment devices, including but not limited to, transverse process hooks, sublaminar hooks, pedicle hooks, fixation plates and other similar devices.
It is well known in the art that coupling multiple fixation systems with a transverse connector also increases strength and stability of the assembly. A transverse connector is used to span the distance between two elongate members. Ideally, the fixation system is implanted in the body so that the two elongate members are substantially parallel to each other in a single plane. This permits the use of a simple transverse connector that need only be adjustable in length, along its longitudinal axis. However, due to variations in body geometries and implanting inconsistencies, the elongate members are rarely parallel in practice. The elongate members may be co-planar but not parallel, or may not be co-planar, or both not co-planar nor parallel. In the past, this problem was addressed by forcefully bending the elongate members or the transverse connector to accommodate for the misalignment of the elongate members. This solution is not optimal because it introduces misalignments that possibly compromise the strength and stability of the assembly. Additionally, it could weaken the mechanical properties of the elongate member or the transverse connector.
Prior inventions addressed this problem through the use of a transverse connector with greater adjustability. U.S. Pat. No. 5,980,523 discloses a transverse connector with separable pieces that are assembled together with separate screw fasteners to accommodate for non-parallel elongate members. The disadvantage with this invention is the number of separable pieces, which are difficult to assemble in the clinical environment, especially considering the miniature sizes of some of the pieces. Surgeons may also risk losing pieces within the patient's body cavity during implantation.
Further advancements solved this problem with the invention of a one-piece transverse connector, but there still remains some shortcomings. For example, U.S. Pat. No. 6,736,817 discloses a one-piece transverse connector that is adjustable for convergent or divergent elongate members, non-coplanar elongate members, and variations in distances between elongate members. The adjustment for convergence or divergence is accomplished through a joint placed between two coupling hooks that attach to elongate members. The joint comprises of two mating surfaces, each with teeth that allows the two ends of the transverse connector to hinge with respect to each other at various angles. The hinge joint is locked with a screw fastener. However, the disadvantage of this design is the complexity of the additional screw. The added screw introduces an additional component for possible failure or user error. Also, the additional weight and bulk of the hinge joint is another drawback of the design. The vertebral fixation assembly may be placed in the human body for extended periods of time. Any tiny additional weight or bulk of the fixation assembly can translate into greater discomfort for the patient. Thus, it is advantageous for the vertebral fixation assembly to be as compact as possible to minimize its intrusion in the body.
As a consequence of the foregoing, there remains a need for improved adjustable transverse connectors with simple, compact adjustments.